Electron discharge device



United States Patent 'ELEC'DRON DISCHARGE DEVICE Cyril L. Day,Huntington, Ind., assignor to International Telephone and TelegraphCorporation, a corporation 0? d.

Application March130, 1953, SerialNo. 345,332

5 Claims. c1, 313-291 The present invention relates to an electrondischarge device andmethod of'making same, and more particularly to sucha device which utilizes cathode and control grid electrodes mounted inclose proximity to each other. In conventional vacuum tubeconstructions, the electrodes comprising the tube, such as the cathode,control grid, and anode, are arranged in suitable geometrical relationwith respect to each other to enable the eifective control of electronflow from the cathode to the anode by means of the control grid which isinterposed in a space between the cathode and anode. The cathode iselectron emissive and may be constituted, for example, by photoelectricor thermally emissive materials, the electrons emitted by the cathodebeing collected by the anode after passing through the space partiallyoccupied by the control grid. In triode tubes, for example, theseelectrons normally flow tothe anode in accordance with the controllingeffect of the control grid. The biasing potential normally appliedtothis grid is varied, in some circuits, to effect substantial currentchanges in the tube anode circuit. By use of the grid electrode, it ispossible to use small control voltages for controlling relatively largequantities of power in the anodecircuit, and the effectiveness of thegridin controlling this power, or the space current between the anodeand cathode, may be represented by a mathematical expressioncharacterized as grid plate transconductance (mutual conductance). Incertain applications of vacuum tubes, it has been found highly desirableto have the highest possible value of grid-plate transconductanceandithas been found that the position of the control grid with respect to thecathode plays an important part in obtaining the desired value of suchtransconductance.

In view of the foregoing, it is an object of this invention to providean electron discharge device having an electrode structure conducing tothe highest possible value of gridplate transconductance.

It is another object of this invention to provide a vacuum tubecqnstructionin which the cathode and control,

gridelectrodes are so arranged with respect to each other that thecontrol grid exercises a maximum of control over the-space dischargecurrentflowing betweenthe cathode and-the anode.

Itis still anotherobject ofthis invention to provide a vacuum tubeconstruction having cathode and control grid electrodes which areuniquelyarranged so as to bring the two electrodes into extremely closeproximity with each other while maintaining direct current electricalseparation therebetween.

It is still anotherobject of this invention to provide, ina vacuum tubeconstruction having control grid and cathode electrodes, a physicalrelationship between the two, electrodes which positions the controlgrid in the electron field adjacent thecathode where most effectivecontrol of the flow of these electrons may be obtained.

It is another object of this invention to provide a method for producinga photosensitive cathode in close proximity to a control grid whereby aninsulating space between the cathode and control grid having anappreciably high resistance to leakage currents may be obtained.

In accordance with the present invention, there is provided a vacuumtube construction-comprised of a supporting member made of insulatingmaterial, a cathode surface provided on said supporting member, spacedconductive elements constituting a control grid provided on said cathodesurface, and insulating spacer coating or elements adhered to theconductive elementsforseparating the grid from the cathode'surface. Thespacer elements are made to such negligible thickness as to providealmost contiguous mounting of the grid on the cathode surface to therebyposition the grid where it will. be most effective.

For a better understanding of the invention, together with other andfurther objects thereof, reference is made to the followingdescriptiontaken in connection with the accompanying drawings and itsscope will be pointed out in the appendedclaims.

In the accompanying drawings:

Fig. 1 isan axial section of an embodiment of the present invention; and

Fig. 2 is an enlarged fragmental section of a portion thereof.

Referring to the drawings, a highvacuum electron discharge device 1 iscomprised of a glass or the like envelope 2 of conventional shape andconstruction and a transparent tubular reentrant supporting member 3which may be made of glass or other suitable material as will appearhereinafter. An annular metal flange 4 made of some suitable materialsuch as Kovar is affixed in the usual manner to the end 5 of theenvelope 2 and another Kovar flange 6 is secured to a radially outwardlyflaring lip 7 on the end of the support3. These flanges 4 and 6 are.suitably secured together such as by seam welding so as to provide asupporting connectionbetween the two members 2 and 3 and to position themember 3 centrally. of the envelope 2. The connections between theflanges 4 and 6 and the respective members 2 and 3 are such as toprovide a hermetic seal for evacuating the space between the support 3and the envelope 2.

The electrode assembly of the tube, which is generally cylindrical inthe illustrated embodiment, is securely mounted on the outerperipheralsurface of the support 3, and suitable wire leads 7a, 8 and 9, connectthe electrodes of this assembly to terminal connections 10, 11 and 12,respectively, projecting through the glass envelope 2;

The electron control electrode assembly, shown in enlarged detail inFig. 2, is comprised of a cathode, generally, indicated by the referencenumeral 13, and a control grid element 14. The cathode itself iscomprised of a first layer of metal 15 such as antimony or silver, whichin the illustrated embodiment is thinenough to permitthe passage oflight therethrough. This layer 15 is adhered to the outer peripheralsurface of the support 3 by the use of any of the usual processes, suchas by evaporation. The control grid 14- is comprised of a wire meshscreen of approximately 500 mesh size, and this screen is preformed to atubular shape so as to fit over the cylindrical layer 15. Beforeassembling the grid 14 on the metallic layer 15, insulating spacers 16are adhered tothe inner:

to' provide the necessary electrical insulation between the cathode base15 and the grid 14. In the preferred arrangement, it is desired tolocate securely the grid 14 as close to the surface of the cathode base15 as possible. Withthe spacers 16 properly secured to "the innerperiphery to the grid 14, "the grid is telescopedovertlie support andlocated axially thereof as shown in Fig. 1. Preferably, the innerdiameter of the grid14determined by the thickness of the spacers 16, issubstantially coextensivewith the outer diameter of the metallic layer15 to provide a snug, secure fit.

The anode 17 is tubular in shape and is centered both axially andcoaxially over the grid electrode 14 by glass or the like spacers 18. Aplurality of tiny perforations 19 are provided in the wall of the anode17 for a purpose which will be explained more fully hereafter. As willbe seen in Fig. 1, the terminal connection is conductively connected tothe anode '17, the cathode base is connected to the terminal 11, and thegrid 14 is connected to'the terminal 12.

In the assembly of the construction thus far described, the cathode base15, the grid 14, and the anode 17 are assembled onto the support 3. Itis important, however, that the grid 14 be cleaned of oxides (by meansof hydrogen furnace or the like) before its assembly onto the tube. Thisassembly may be accomplished in the open atmosphere, the importance ofwhich being explained more fully hereinafter. The support 3 with itselectrode assembly is now located within the envelope 2 as shown in Fig.l, and the flanges 4 and 6 are seam- Welded to provide a vacuum tightcontainer. The tube is next evacuated in the customary manner.

As a final step in the method of fabricating this tube, cesium vapor isintroduced into the tube by the use of the conventional techniques fordepositing on the cathode base 15 (via the perforations 19), within theelemental areas 20 bordered by the various spacers or coating 16, acoating of cesium for making the cathode photosensitive. Irradiation ofthe elemental areas 20 will result in the emission of electrons which isdirected radially outwardly through the grid openings.

In fabrication, it is important that the surface of the grid 14 be suchas will not permit the adherence thereto or chemical reaction therewithof the cesium vapor, and as a corollary, the conductive material of thecathode base 15 must be of such constituency (such as antimony oxide) aswill combinewith the cesium vapor so as to provide the electron emissiveareas Ztl as previously described. With the cathode base 15 beingcomprised of either silver oxide or antimony oxide, and the grid 14being composed of a material such as copper or nickel cleaned of itsoxide surface, the cesium will adhere and react only with the cathodebase.

This precleaning of the grid is important because in the photoelectrictube, if the cesium adheringly deposits onto the grid 14, the gridbecomes electron emissive which would defeat the normal function of thevacuum tube. cathode base will be made electron emissive therebyproviding the normal physical relationship between the cathode andcontrol grid electrodes.

As mentioned earlier,-the spacers or coatings 16 are of minimumthickness, that is, the spacers 16 are of such thickness as to positionthe grid 14 almost directly upon the surface of the cathode base 15 yetthick enough to provide electrical separation therebetween; It has beenfound that the control grid is most effective when the electric field ofthe grid is located immediately adjacent the emitting surface of thecathode, and from the description of the foregoing, it Will be seen thatsuch field is positioned as close to the emitting surface of the cathodeas appears to be possible.

In operation, electrons are emitted from the cathode surface, and thosewhich possess sufiicient velocity to pass beyond the negatively chargedgrid are accelerated By following the preceding procedure, only the-2,894,167 7, p r .1 1 m toward the anode. Most effective control of thisflow of electrons is achieved by positioning the control grid as closelyto the cathode surface as possible.

As mentioned earlier, the electrode assembly is mounted on the supporttube 3 in the open atmosphere. The proper treatment of the gridmaterial, as explained hereinbefore, makes this arrangement of assemblypossible, the cesiation step in the method of fabrication serving tosensitize only the elemental areas 20 on the cathode base 15 and noother portion of the assembly.

In other prior art tube arrangements, silver oxide usually constitutesthe surface upon which the cesium is deposited, the silver oxide coatingusually covering both the grid and cathode base materials. Thus, whenthe cesium vapor is introduced into the evacuated envelope, both thegrid and cathode surfaces are sensitized thereby reducing the operatingefficiency of the finished tube. With the present arrangement,deposition of cesium takes place only on thebase material 15.

From the foregoing it will be apparent that the grid electrode hasnegligible but adequate spacing with re-. spect to the cathode 13, andthat the grid is mounted rigidly with rmpect to the cathode. Such rigidmounting reduces the tendency of the grid to move relative;

to the cathode and to thereby develop microphonicsf Also, it is obviousthat the present tube will withstand severe jarring and vibration whichcauses conventionaltubes to be noisy.

In the operation of the foregoing described embodiment, a lamp orsimilar light source is introduced in to. the reentrant support 3 toirradiate the photoelectric areas 20 from which electrons flow radiallyoutwardly through the openings in the grid 14 to the anode 17;; While aphotoelectric tube has been illustrated and de-;

scribed, it will appear obvious to those skilled in the art that thebase 15 may be composed of silver treated in any well known manner tomake it thermally emissive.-

While there has been described what is at presentconsidered thepreferred embodiment of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims, to cover all such changes andvmodifications as fall within the true spirit and scope of),

the invention.

What is claimed is:

1. An electron flow-controlling assembly for an electron dischargedevice comprising an insulating support,

and comprising a screen-like member having apertures, insulation adheredto one side only of said screen-like member, said insulation contactingsaid layer and con-' stituting a support and spacer for said screen-likememher, and electron-emissive material provided only on.

the elemental areas of said layer which are not contacted by saidinsulation thereby providing intimately close butinsulated spacingbetween such areas and said controlgrid element.

2. An electron-flow-controlling assembly for an elecductively connectedspaced metallic wire-like elements,

said elements being formed of metal selected from the group consistingof copper and nickel, insulating spacers separating said wire-likeelements from said layer, said spacers contacting said layer at pointsdirectly beneath,v said wire-like elements, the elemental areas of saidlayer which are not contacted by said spacers only being electronemissive thereby providing intimately close but insulated spacingbetween such areas and said controlgrid element.

3. The method of fabricating an electron discharge control assembly inthe atmosphere comprising the steps of providing a base of conductivematerial on a supporting member, adhering an insulating material to oneside of a control-grid element, mounting said control grid element onsaid supporting member with said insulating material directly contactingsaid conductive material, and activating the elemental areas of saidconductive material which are not contacted by said insulation materialto render said areas only electron-emissive.

4. The method of fabricating an electron discharge control assembly inthe atmosphere comprising the steps of providing a base of conductivematerial on a supporting member, adhering an insulating material to oneside of a control-grid element, treating the control-grid element toremove oxide coating therefrom, mounting said control-grid element onsaid supporting member with said insulating material directly contactingsaid conductive material, and the elemental areas of said conductivematerial which are not contacted by said insulation material to rendersaid areas only electron-emissive.

5. The method of fabricating an electron discharge control assembly inthe atmosphere comprising the steps of providing a base of conductivematerial on a supporting member, said conductive material being one ofthe group of antimony and silver, adhering an insulating material to oneside of a control-grid element, said control grid element being composedof a material selected from the group of copper and nickel, treating thecontrol-grid element to remove oxide coating therefrom, mounting saidcontrol-grid element on said conductive material whereby the insulatingmaterial separates the two, and subjecting the assembly to casium vapor,said cesium vapor adhering to said base but not to said element therebyrendering said base electron-emissive.

References Cited in the file of this patent UNITED STATES PATENTS1,839,899 Slepian Jan. 5, 1932 1,861,637 Marden et a1. June 7, 19321,942,501 Stillwell Jan. 9, 1934 1,965,849 McIlvaine July 10, 19342,120,916 Bitner June 14, 1938 2,290,748 Hergenrother July 21, 19422,601,024 Jacobs et a1 June 17, 1952 FOREIGN PATENTS 115,700 GreatBritain May 21, 1918

